1. Field of the Invention
The invention relates to a knife for cataract surgery.
2. Description of the Prior Art
Over the years, the incision in cataract surgery has become progressively smaller. Whereas in the past the larger cataract incisions were created using a combination of a knife and scissors, current cataract incisions can be made solely with the use of a keratotomy knife which in common surgical techniques creates an incision from approximately 2.5 to 3.5 mm in width. Incisions are made in a variety of techniques and locations including. 1). Scleral tunnel in which a partial thickness Scleral incision is made approximately 2 mm posterior to the corneosceral junction, and is dissected anteriorly into clear cornea where the anterior chamber is entered using a sharp tipped keratotomy knife. 2). A limbalxe2x80x94xe2x80x9cnear clearxe2x80x9d which is begun at the corneo-scleral junction and carried into clear cornea where again the anterior chamber is entered using a sharp keratotomy knife. 3). Clear corneal incisionxe2x80x94in which the cornea is entered anterior to the cornea-scleral junction so that only clear cornea is involved in the incision structure. Again the anterior chamber is entered using a sharp pointed keratotomy knife.
All of these incisions have several characteristics in common. First, they are relatively small, both in width and length. Secondly, all incisions end by entering the anterior chamber through clear cornea. Because these incisions are small, they can be created so that they are self-sealing and do not require suturing. Since they are intended and expected to be self-sealing and water tight to prevent leakage of fluid from the anterior chamber of the eye, it is critical that a reliable, repeatable and appropriately shaped incision be made to prevent vision threatening post-operative complications associated with wound leakage such as infection, and hypotony.
The current commonly used keratotomy blade configurations incorporate certain design characteristics which can result in a less than desirable, and less than ideal incision which may leak due to poor architecture in its creation. More specifically, the common sharp tipped keratotomy does not routinely create, an entry sight into the anterior chamber in a linear fashion, but can cause the incision to extend inadvertently posteriorly toward the limbus thereby creating a less than ideal floor to the incision which may not seal, and may allow aqueous leakage. This posterior extension of the incision is caused by the fundamental design characteristics of the blade tip, and is to a considerable extent independent of surgical expertise in using the blade. Therefore, using this particular blade design, a certain percentage of the incisions will leak due to poor wound architecture from extension of the wound posteriorly.
Another problem with current keratotomy blade designs is that they can inadvertently create a wider than desired incision if the blade is introduced or removed from the incision in a sideways fashion that is not parallel to the original axis of the incision thereby enlarging the wound due to the sharp edges of the sides of the blades. This inadvertent widening of the wound will create a larger wound that leaks not only postoperatively, but intra-operatively during cataract extraction particularly with phaco emulsification where the wound is larger than the phaco emulsification tip thereby allowing egress or outflow of fluid around the tip to an undesirable degree. In modern cataract surgery with phaco emulsification, this fluid egress is a problem since it is desirable to have the wound be water tight during phaco emulsification so that control of the intraocular structures can be maintained throughout the procedure in a more precise fashion. Any leakage around the phaco tip is undesirable. Therefore as can be seen and as is described above, current existing cataract incision knives (keratotomy knives) do not routinely and reliably create ideal water tight self-sealing incisions.
It is an object of the invention to provide new keratotomy knife tip designs that eliminate the above described problems of inadvertent posterior extension of the wound, and inadvertent widening of the wound. The knife design of one embodiment (FIGS. 1-6) has a sharp central tip that extends backward only a short distance at which point it encounters a redirection of the sharp cutting blade at the xe2x80x9cshoulderxe2x80x9d. By redirecting the sharp cutting edge from a backward to a sideways oriented direction, the cutting edge creates an incision that is essentially linear and parallel to the limbus thereby eliminating the possibility of posterior extension of the wound. Additionally, the side edges of the blade that extend backward from the redirectedxe2x80x94horizontal cutting edge, are blunt. By making the side edges of the blade blunt, no cutting or enlarging of the width of the wound will occur, thereby preventing inadvertent enlargement of the wound width if the blade is not introduced or withdrawn in a direction that is absolutely parallel to the incision axis. Therefore, with the keratotomy knife tip configuration here presented, posterior extension of the wound is completely eliminated as is inadvertent enlarging of the wound width. Also, the sharp cutting edges will possibly have a bevel to facilitate their introduction into the anterior chamber with minimal force and maximum smoothness and accuracy,
A second embodiment, (FIGS. 7-12) comprises a keratotomy knife with a penetrating sharp cutting tip point with the cutting edge located on the more central side of the blade again extending backwards a short distance at which point the xe2x80x9cshoulderxe2x80x9d redirects the cutting blade again in a direction almost perpendicular to the direction of introduction into tissue. The side edges of this blade are similarly blunt and unable to cut tissue. This knife tip configuration allows for entry into the anterior chamber through the corneal tissue at the point of the tip and allows is a posterior, backward extension of the incision for only a very short distance at which point the cutting is abruptly redirected in a direction essentially parallel to the limbus. This design characteristic will completely eliminate the undesired posterior extension of the wound toward the limbus during cutting. Since the side edges again are blunt, the wound cannot be inadvertently enlarged by introducing or withdrawing the knife in a direction not parallel to the incision axis.
Therefore, the two herein disclosed keratotomy knife tip configurations both have the design characteristics of eliminating undesirable posterior extension of the wound, and inadvertent widening of the wound thereby more reliably creating self-sealing incisions.
An additional desirable feature of these keratotomy tip designs relates to surgical technique. It is common practice by many surgeons to initiate the incision making process by creating a partial thickness cut-down into the corneal or scleral tissue. After the partial thickness corneal, corneal or scleral cut-down is made, a tunnel is dissected anteriorly to eventually arrive in the clear cornea at which point the anterior chamber is entered. The depth of the initial cut-down is somewhat variable and subject to surgical skill and experience. When using the keratotomy knife tip designs disclosed here, the problem of variability of the depth of the cut down can be eliminated in the following way: The knife tip is introduced perpendicular to the ocular surface and pressed into the tissue cutting until the xe2x80x9cshoulder or shouldersxe2x80x9d of the blade are reached. Once the shoulders have been barely introduced into the tissue, the blade is then redirected in a forward fashion creating a tunnel of the desired depth, the depth being accuratley and reproducibly established by the distance between the sharp tipped point, and the shoulder. By using the distance between the tip of the keratotomy knife which is first introduced into the tissues, and the shoulders as the final judge for depth of introduction of the blade into the tissues, a reliable depth for introduction of the blade is created, the distance between the tip and shoulders acting as a reliable gauge for depth of penetration of the blade into the tissues. Once the depth of penetration of the blade tip into the tissues has reached the level of the shoulder, the blade is redirected so that the blade is in a plane almost parallel to the iris. With the knife in this orientation, the tunnel is created by pushing the blade forward into the clear cornea to the desired extent after which time the blade tip is redirected again toward the anterior chamber where the last deep layers of cornea including the endothelium are penetrated and cut leaving a linear incision in the endothelium that is virtually parallel to the limbus with no posterior extension. The blunt blade sides will prevent inadvertent enlargement of the wound even with inadvertent side to side movement of the knife during reorientation of the blade during the incision process. This is true of both the center point tip configuration, and the side point configuration.